FUEL PUMP TEST 2: Fuel Pressure Test With Gauge
As mentioned at the beginning of this tutorial, Ford has made it easy to test the fuel pump with a fuel pressure gauge... since you'll find a Schrader valve on the fuel injector rail that you can connect a fuel pressure gauge to (see photo of location here Location Of The Fuel Pressure Schrader Valve Test Port).
Using a fuel pressure gauge is one of the most accurate ways to make sure that enough fuel is reaching the fuel injectors. If you do own a fuel pressure gauge, this is the test for you.
If you don't own one, you can run down to your local Auto Zone or O'Reilly auto parts store and borrow one from them (for a small cash deposit, which you'll get back when you return the tool).
If you're interesting in buying one, take a look at my recommendations here: Which And Where To Buy A Fuel Pressure Gauge.
OK, let's get started with this test:
Connect the fuel pressure gauge to the Schrader valve on the fuel rail.
When ready, ask your helper to crank the engine while you observe the fuel pressure tester's gauge.
Your fuel pressure gauge will register one of the two following results:
1.) The fuel pressure gauge will register 35 PSI, or
2.) The fuel pressure gauge will register 0 PSI.
OK, now that the testing part is done... let's take a look at what your results mean:
CASE 1: If the fuel pressure gauge registered 0 PSI This confirms that the cause of your 4.0L Ford Explorer (Ranger, Aerostar, Mountaineer) is caused by a lack of fuel.
Now, I usually take two more precautions, before condemning the fuel pump as BAD... and this is to check:
- That the fuel pump inertia switch isn't activated and cutting power to the fuel pump. For more info on this take a look at the next section: Checking The Fuel Pump Inertia Switch.
- If the fuel pump inertia switch is OK, then I still make sure that the fuel pump is getting 12 Volts as the engine is cranking. This is just to make sure that the fuel pump relay and fuse are OK and doing their job.
To check that the fuel pump is getting power (after the inertia switch has been checked) you'll need to attach a multimeter in Volts DC mode to the wire that supplies this voltage to the fuel pump and while a helper cranks the engine... verify that the fuel pump is getting this power. If the 12 Volts are being supplied to the fuel pump... you have now 100% verified that the fuel pump is fried and needs to be replaced.
CASE 2: If the fuel pressure gauge registered 35 PSI: This fuel pressure gauge result let's you know that the fuel pump is working and delivering enough fuel to the fuel injectors. The reason your 4.0L Ford vehicle is not starting is due to another reason. The fuel pump is OK.
I suggest you take a look at the following tutorial: How To Troubleshoot A No Start (Ford 4.0L), to see more testing options.
Location Of The Fuel Pressure Schrader Valve Test Port
The Schrader Valve, on the 4.0L Ford V6 engine is located on the injector fuel rail. To be a bit mores specific, it's on the passenger side of the engine between the ignition coil pack and the upper radiator hose.
In the photo above, it's shown without its plastic cap.
Checking The Fuel Pump Inertia Switch
Your 4.0L Ford Explorer (Ranger, Aerostar, or Mercury Mountaineer) comes equipped with a fuel pump inertia switch, whose job is to cut power (or ground) to the fuel pump in case of an impact... which causes the engine to stall (if it was running) or for the engine to crank but not start due to a lack of fuel.
Although it's designed to activate during a severe impact caused by an automobile accident... sometimes it gets activated by less than severe impacts (and this happens a lot).
This means that it's always a good idea to check and reset the inertia switch whenever testing the fuel pump. On the majority of the vehicles covered by this tutorial, the inertia switch is located below the right side of the instrument panel, behind the trim panel.
Resetting the fuel pump inertia switch simply involves pushing down on the button located on top of the inertia switch till it bottoms out. If the inertia switch has been jolted into shutting off the fuel pump... you'll feel a definite ‘click’ as you depress the button.